The goal of this project is to determine the role of transforming growth factor-alpha (TGF-alpha) in colon carcinoma cell growth. Colon cancer is a leading cause of death in the United States and an understanding of the growth control mechanisms involved in colon cancer would be useful in the development of new therapeutic agents. A model system consisting of human colon carcinoma cell lines which vary in their degree of differentiation, growth properties, growth factor requirements, and several other biochem- ical and biological properties will be utilized in these studies. These cell lines vary in their response to exogenous epidermal growth factor(EGF). In general, the EGF-responsive cell lines have a higher number of EGF receptors (EGF-R) and produce less TGF-a then the EGF-non-responsive lines. The TGF-alpha produced by representative cell lines will be quantitated and characterized with respect to molecular weight. The TGF-alpha mRNA levels will be determined under various growth conditions and correlated to TGF-a protein production. Antibodies directed against TGF-a and the EGF-R will be used in attempts to block the action of TGF-alpha on the cells to determine if the cells utilize endogenous TGF-alpha in an autocrine manner. The effects on growth rate and growth factor requirements will be examined. The effects of chemical differentiation agents EGF, and transforming growth factor Beta on the levels of TGF-alpha and the properties of the EGF-R will be examined. This will allow determination of any reciprocal changes which may occur between TGF-alpha and its membrane receptor, the EGF-R. Cells which are responsive to exogenous EGF will be transfected with a synthetic EGF gene to determine if endogenous production of EGF can eliminate the growth response to exogenous EGF. These experiments will provide information concerning the autocrine role of TGF-alpha in colon carcinoma cell growth. If TGF-alpha acts in an autocrine manner. agents which disrupt the autocrine circuit may be useful in blocking malignant cell growth.